实现DES加解密算法实验报告
一、 DES加解密算法问题简介
DES算法全称为Data Encryption Standard,即数据加密算法,它是IBM公司于1975年研究成功并公开发表的。DES算法的入口参数有三个:Key、Data、Mode。其中Key为8个字节共64位,是DES算法的工作密钥;Data也为8个字节64位,是要被加密或被解密的数据:Mode为DES的工作方式,有两种:加密或解密。
二、 DES加解密算法设计方法简介
DES算法把64位的明文输入块变为64位的密文输出块,它所使用的密钥也是64位,其功能是把输入的64位数据块按位重新组合,并把输出分为L0 、R0两部分,每部分各长32位,其置换规则见下表:
58,50,12,34,26,18,10,2,60,52,44,36,28,20,12,4,
62,54,46,38,30,22,14,6,64,56,48,40,32,24,16,8,
57,49,41,33,25,17, 9,1,59,51,43,35,27,19,11,3,
61,53,45,37,29,21,13,5,63,55,47,39,31,23,15,7,
即将输入的第58位换到第一位,第50位换到第2位,……,依此类推,最后一位是原来的第7位。 L0、R0则是换位输出后的两部分,L0是输出的左32位,R0 是右32位,例:设置换前的输入值为D1D2D3……D64,则经过初始置换后的结果为:L0=D550……D8;R0=D57D49...D7。
经过26次迭代运算后,得到L16、R16,将此作为输入,进行逆置换,即得到密文输出。逆置换正好是初始置的逆运算,例如,第1位经过初始置换后,处于第40位,而通过逆置换,又将第40位换回到第1位,其逆置换规则如下表所示:
40,8,48,16,56,24,64,32,39,7,47,15,55,23,63,31,
38,6,46,14,54,22,62,30,37,5,45,13,53,21,61,29,
36,4,44,12,52,20,60,28,35,3,43,11,51,19,59,27,
34,2,42,10,50,18,58 26,33,1,41, 9,49,17,57,25,
放大换位表
32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9, 8, 9, 10,11,
12,13,12,13,14,15,16,17,16,17,18,19,20,21,20,21,
22,23,24,25,24,25,26,27,28,29,28,29,30,31,32, 1,
单纯换位表
16,7,20,21,29,12,28,17, 1,15,23,26, 5,18,31,10,
2,8,24,14,32,27, 3, 9,19,13,30, 6,22,11, 4,25,
在f(Ri,Ki)算法描述图中,S1,S2...S8为选择函数,其功能是把6bit数据变为4bit数据。下面给出选择函数Si(i=1,2......8)的功能表:
选择函数Si
S1:
14,4,13,1,2,15,11,8,3,10,6,12,5,9,0,7,
0,15,7,4,14,2,13,1,10,6,12,11,9,5,3,8,
4,1,14,8,13,6,2,11,15,12,9,7,3,10,5,0,
15,12,8,2,4,9,1,7,5,11,3,14,10,0,6,13,
S2:
15,1,8,14,6,11,3,4,9,7,2,13,12,0,5,10,
3,13,4,7,15,2,8,14,12,0,1,10,6,9,11,5,
0,14,7,11,10,4,13,1,5,8,12,6,9,3,2,15,
13,8,10,1,3,15,4,2,11,6,7,12,0,5,14,9,
S3:
10,0,9,14,6,3,15,5,1,13,12,7,11,4,2,8,
13,7,0,9,3,4,6,10,2,8,5,14,12,11,15,1,
13,6,4,9,8,15,3,0,11,1,2,12,5,10,14,7,
1,10,13,0,6,9,8,7,4,15,14,3,11,5,2,12,
S4:
7,13,14,3,0,6,9,10,1,2,8,5,11,12,4,15,
13,8,11,5,6,15,0,3,4,7,2,12,1,10,14,9,
10,6,9,0,12,11,7,13,15,1,3,14,5,2,8,4,
3,15,0,6,10,1,13,8,9,4,5,11,12,7,2,14,
S5:
2,12,4,1,7,10,11,6,8,5,3,15,13,0,14,9,
14,11,2,12,4,7,13,1,5,0,15,10,3,9,8,6,
4,2,1,11,10,13,7,8,15,9,12,5,6,3,0,14,
11,8,12,7,1,14,2,13,6,15,0,9,10,4,5,3,
S6:
12,1,10,15,9,2,6,8,0,13,3,4,14,7,5,11,
10,15,4,2,7,12,9,5,6,1,13,14,0,11,3,8,
9,14,15,5,2,8,12,3,7,0,4,10,1,13,11,6,
4,3,2,12,9,5,15,10,11,14,1,7,6,0,8,13,
S7:
4,11,2,14,15,0,8,13,3,12,9,7,5,10,6,1,
13,0,11,7,4,9,1,10,14,3,5,12,2,15,8,6,
1,4,11,13,12,3,7,14,10,15,6,8,0,5,9,2,
6,11,13,8,1,4,10,7,9,5,0,15,14,2,3,12,
S8:
13,2,8,4,6,15,11,1,10,9,3,14,5,0,12,7,
1,15,13,8,10,3,7,4,12,5,6,11,0,14,9,2,
7,11,4,1,9,12,14,2,0,6,10,13,15,3,5,8,
2,1,14,7,4,10,8,13,15,12,9,0,3,5,6,11,
子密钥Ki(48bit)的生成算法
初始Key值为64位,但DES算法规定,其中第8、16、......64位是奇偶校验位,不参与DES运算。故Key 实际可用位数便只有56位。即:经过缩小选择换位表1的变换后,Key 的位数由64 位变成了56位,此56位分为C0、D0两部分,各28位,然后分别进行第1次循环左移,得到C1、D1,将C1(28位)、D1(28位)合并得到56位,再经过缩小选择换位2,从而便得到了密钥K0(48位)。依此类推,便可得到K1、K2、......、K15,不过需要注意的是,16次循环左移对应的左移位数要依据下述规则进行: 循环左移位数1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1
以上介绍了DES算法的加密过程。 DES算法的解密过程是一样的,区别仅仅在于第一次迭代时用子密钥K15,第二次K14、……,最后一次用K0,算法本身并没有任何变化。
三、 程序代码
#include "memory.h"
#include "stdio.h"
enum {encrypt,decrypt};//ENCRYPT:加密,DECRYPT:解密
void des_run(char out[8],char in[8],bool type=encrypt);
//设置密钥
void des_setkey(const char key[8]);
static void f_func(bool in[32],const bool ki[48]);//f函数
static void s_func(bool out[32],const bool in[48]);//s盒代替
//变换
static void transform(bool *out, bool *in, const char *table, int len);
static void xor(bool *ina, const bool *inb, int len);//异或
static void rotatel(bool *in, int len, int loop);//循环左移
//字节组转换成位组
static void bytetobit(bool *out,const char *in, int bits);
//位组转换成字节组
static void bittobyte(char *out, const bool *in, int bits);
//置换IP表
const static char ip_table[64]={58,50,42,34,26,18,10,2,60,52,44,36,28,20,12,4,62,54,46,38,30,22,14,6,64,56,48,40,32,24,16,8,57,49,41,33,25,17,9,1,59,51,43,35,27,19,11,3,61,53,45,37,29,21,13,5,63,55,47,39,31,23,15,7};
//逆置换IP-1表
const static char ipr_table[64]={40,8,48,16,56,24,64,32,39,7,47,15,55,23,63,31,38,6,46,14,54,22,62,30,37,5,45,13,53,21,61,29,36,4,44,12,52,20,60,28,35,3,43,11, 51,19,59,27,34,2,42,10,50,18,58,26,33,1,41,9,49,17,57,25};
//E 位选择表
static const char e_table[48]={32,1, 2, 3, 4, 5,4, 5, 6, 7, 8, 9,8, 9, 10,11,12,13,12,13,14,15,16,17,16,17,18,19,20,21,20,21,22,23,24,25,24,25,26,27,28,29,28,29,30,31,32,1};
//P换位表
const static char p_table[32]={16,7,20,21,29,12,28,17,1,15,23,26,5,18,31,10,2,8,24,14,32,27,3,9,19,13,30,6,22,11,4,25};
//pc1选位表
const static char pc1_table[56]={
57,49,41,33,25,17,9,1,
58,50,42,34,26,18,10,2,
59,51,43,35,27,19,11,3,
60,52,44,36,63,55,47,39,
31,23,15,7,62,54,46,38,
30,22,14,6,61,53,45,37,
29,21,13,5,28,20,12,4
};
//pc2选位表
const static char pc2_table[48]={
14,17,11,24,1,5,3,28,
15,6,21,10,23,19,12,4,
26,8,16,7,27,20,13,2,
41,52,31,37,47,55,30,40,
51,45,33,48,44,49,39,56,
34,53,46,42,50,36,29,32
};
//左移位数表
const static char loop_table[16]={1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1};
//S盒
const static char s_box[8][4][16]={
//s1
14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7,
0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8,
4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0,
15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13,
//s2
15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10,
3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5,
0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15,
13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9,
//s3
10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8,
13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1,
13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7,
1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12,
//s4
7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15,
13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9,
10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4,
3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14,
//s5
2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9,
14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6,
4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14,
11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3,
//s6
12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11,
10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8,
9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6,
4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13,
//s7
4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1,
13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6,
1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2,
6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12,
//s8
13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7,
1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2,
7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8,
2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11
};
static bool subkey[16][48];//16圈子密钥
void des_run(char out[8],char in[8], bool type)
{
static bool m[64],tmp[32],*li=&m[0], *ri=&m[32];
bytetobit(m,in,64);
transform(m,m,ip_table,64);
if(type==encrypt){
for(int i=0;i<16;i++){
memcpy(tmp,ri,32);
f_func(ri,subkey[i]);
xor(ri,li,32);
memcpy(li,tmp,32);
}
}else{
for(int i=15;i>=0;i--){
memcpy(tmp,li,32);
f_func(li,subkey[i]);
xor(li,ri,32);
memcpy(ri,tmp,32);
}
}
transform(m,m,ipr_table,64);
bittobyte(out,m,64);
}
void des_setkey(const char key[8])
{
static bool k[64], *kl=&k[0], *kr=&k[28];
bytetobit(k,key,64);
transform(k,k,pc1_table,56);
for(int i=0;i<16;i++)
{
rotatel(kl,28,loop_table[i]);
rotatel(kr,28,loop_table[i]);
transform(subkey[i],k,pc2_table,48);
}
}
void f_func(bool in[32],const bool ki[48])
{
static bool mr[48];
transform(mr,in,e_table,48);
xor(mr,ki,48);
s_func(in,mr);
transform(in,in,p_table,32);
}
void s_func(bool out[32],const bool in[48])
{
for(char i=0,j,k;i<8;i++,in+=6,out+=4)
{
j=(in[0]<<1)+in[5];
k=(in[1]<<3)+(in[2]<<2)+(in[3]<<1)+in[4];
bytetobit(out,&s_box[i][j][k],4);
}
}
void transform(bool *out,bool *in,const char *table,int len)
{
static bool tmp[256];
for(int i=0;i<len;i++)
tmp[i]=in[table[i]-1];
memcpy(out,tmp,len);
}
void xor(bool *ina,const bool *inb,int len)
{
for(int i=0;i<len;i++)
ina[i]^=inb[i];
}
void rotatel(bool *in,int len,int loop)
{
static bool tmp[256];
memcpy(tmp,in,loop);
memcpy(in,in+loop,len-loop);
memcpy(in+len-loop,tmp,loop);
}
void bytetobit(bool *out,const char *in,int bits)
{
for(int i=0;i<bits;i++)
out[i]=(in[i/8]>>(i%8)) &1;
}
void bittobyte(char *out,const bool *in,int bits)
{
memset(out,0,(bits+7)/8);
for(int i=0;i<bits;i++)
out[i/8]|=in[i]<<(i%8);
}
void main()
{
char key[8]={'p','r','o','g','r','a','m'},str[8];
puts("*****************DES***********************");
printf("\n");
printf("\n");
puts("请输入;");
gets(str);
printf("\n");
puts("****************************************");
des_setkey(key);
des_run(str,str,encrypt);
puts("加密后:");
puts(str);
printf("\n");
puts("****************************************");
puts("解密后:");
des_run(str,str,decrypt);
puts(str);
printf("\n");
puts("****************************************");
printf("\n");
}
四、 算法介绍
DES算法的入口参数有三个:Key、Data、Mode。其中Key为8个字节共64位,是DES算法的工作密钥;Data也为8个字节64位,是要被加密或被解密的数据;Mode为DES的工作方式,有两种:加密或解密。
DES算法是这样工作的:如Mode为加密,则用Key 去把数据Data进行加密, 生成Data的密码形式(64位)作为DES的输出结果;如Mode为解密,则用Key去把密码形式的数据Data解密,还原为Data的明码形式(64位)作为DES的输出结果。在通信网络的两端,双方约定一致的Key,在通信的源点用Key对核心数据进行DES加密,然后以密码形式在公共通信网(如电话网)中传输到通信网络的终点,数据到达目的地后,用同样的Key对密码数据进行解密,便再现了明码形式的核心数据。
五、 实验数据
输入数字:1357
六、 实验结果
七、 实验体会
本学期的实验上机课对我来说最大的体会就是了解了DES算法,大致了解了它的基本原理,在编写的过程中虽然遇到了很多的错误,但是最后也在自己的反复检查、修改后将程序实现了。我想这就是对我来说最有成就感的事情。